Track circuit



March 14, 1961 R. c. RENICK ErAL 2,975,272

TRACK CIRCUIT Filed April 2, 1957 By MM5-fm Attorney- United States Patentv'lOfice TRACK CIRCUIT Robert C. Renick, Plainfield, NJ., and Claude I. Pasquier,

Long Island City, N.Y., assignors to International Telephone and Telegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Apr. 2, 1957, Ser. No. 650,174 s claims. (c1. 246-34) This invention relates to a track circuit for indicating the condition of a track section, such, for example, as l the track section is unoccupied and in good condition.

A train present on the track section completes a circuit between the rails thereby shunting the relay andi causing =it to drop to indicate the presence of the train. vAbroken rail opens the circuit, which also causes the relay to drop.

Several difiiculties are experienced with the above systern such as poor insulation between the rails causing high leakage currents which are indistinguishable from the effect of a shunt caused by a train. This difficulty has become more severe with the introduction of lighter rolling stock and disc-type brakes which do not exert a cleaning action along the wheel tread, resulting in a relatively high resistance shunt produced by the train which cannot be distinguished from these leakage currents if the track section is long. Because of this, it has been necessary to limit. the length of track covered by each track circuit, since the leakage current increases with length.

' Various attempts have been made to increase the length of track over which reliable operation may be obtained. For example, alternating current energy has been employed, either pulsed or continuous. Some improvement is thereby obtained because capacitive coupling between rail and wheel is used to advantage when an insulating film prevents good conduction, but the current leakage imposes an upper limit to the length of track over which this improvement is significant.

The prinicipal object of this invention is to provide an improved track circuit.

Another object is to provide a track circuit which permits reliable operation with a longer track section than has been heretofore possible.

According to a main feature of the invention, a track circuit is provided which overcomes the problem of leakage from the rails to ground by coupling a 'source of energy, preferably alternating current, at one end of the track section between one rail and ground and coupling a detecting `arrangement at the other end of the track section 4between the other rail and ground, to indicate the presence of a train when the level of energy coupled between the rails exceeds a threshold value. With this arrangement only the ungrounded leakage current flows through the detector.

In the preferred form of the invention two frequency sources of electrical energy and two detectors are used, each rail having a different one of said frequency sources 2,975,272 vPatterned Maa-14 196i coupled between one end and ground, a detector coupled between the other end and ground, each detector being tuned to the frequency supplied to the opposite rail. f

According to another feature, each rail has an additional detector coupled between it and ground, tuned to the frequency supplied to that rail, for determining rail continuity and registering an alarm condition when the signal is greatly reduced.

The above-mentioned and other features and objects of `this invention will become more apparent by reference to the following description taken in conjunction .with the accompanying drawing, in which the single figure is a block and schematic diagram of a preferred embodiment of the invention showing a track and associated track circuit.

Referring now to the drawing, a track section 1A has rails 2 and 3 which are insulated from adjacent track sections by insulators 4. The track ballast and ties (not shown) produce leakage resistance between the rails, represented by resistance 5; and from each of the rails t0 ground, represented by resistances 6 and 7, respectively. At one end of the track section sources of alternating current energy are coupled to the rails, represented by generator 8 coupled between rail 2 and ground and generator 9 coupled between rail 3 andground. The output' of these generators is preferably at separate frequencies :(Fl and F2) in the audio range, generator 8 having an output at a first frequency (F1) and-generato'rQ having an output at a second frequency (F2). vAt the otheren'd of the track section detectors 10"and 11 are coupled between rail 2 and ground and detectors 12 and 13 lare coupled between rail 3 and ground. These'detectors may comprise filters 14 to 17, respectively, amplifiers 18 to 21, respectively, and relays 22 to 25, respectively. In each detector the filter is coupled between the rail and the input of the amplifier, and the relay is coupled to the output of the amplifier. Filter 14 of detector 10 and filter 16 of detector 12 pass the first frequency (F1), while filter 15 of detector 11and filter 17 of detector 13 the second frequency (F2).' The amplifiers 18 to 21 are preferably of the transistor type designed to 'have 'a substantial direct-current component in their outputjproportional to the amplitude of the alternating current input, to operate the respective D.C. operated relays 22 rto25; alternatively the amplifiers 18 to 21 may produce an A.C. output and the relays may be of the alternating current type. Another possibility is to include rectifiers between the amplifiers and the relays.

In the normal condition, the signals at frequency (F1) from generator 8, over rail 2, through detector 10 and the ground return, are at a sufficient level to maintain relay 22 operated and its break contacts open; and the signals at frequency F2 from generator 9 over rail 3, through detector 13 and the ground return are at a sufficient level to maintain relay 25 operated and its break contacts open.

In the event of a circuit interruption, such as broken rail, between generator 8 and detector 10, or between generator 9 and detector 13, the corresponding relay 22 or 25 will be released, and at its contacts connect wire 26 to ground to register an alarm condition in equipment 27.

Equipment 27 is the usual control equipment, which may be used to transmit indication signals to a centraltrain-control station, or control signals to equipment suchl signal current at the second frequency from generator v.9,.over rail 3, through leakage resistance 5, to rail 2 and thence to detector 11 and ground. However, the threshold level of the circuit is so adjusted, for example, by providing a threshold in ampliers 19 and 20 or in relays 23 yand 24, that relays .23 and 24 do not operate under this jcondition. Signal current 'ow in the leakagetoground resistances 6 and 7 is returned through the -ground path to :the generators without flowingthrough any of the .detectors 10to 13. Thefground :plane .acts .as a shield to reduce cross coupling Abetween the rails.

.This permits .the length .of track section 1 to be made longer than could be achieved .inprior arrangements, beffore ,the cross-coupling exceeds the maximum thresholdzvalue allowable zfor reliable operation.

`When a trainis present ontrack section 1, crosscoupling betweenrails v2 and 3 is substantially increased. If fa lm on the rails or wheels prevents good conduction, capacitive coupling betweenthe rails and wheels increases the coupling, since audio frequency signals are used. Suicient current now flows from generator 8 to detector 12, .and from generator 9 to detector 11, to exceed the threshold and operate the respective relays 23 .and 24. Wire 28 is connected to ground at the make contacts a of both relays 23 and 24, to register a track occupied condition in control equipment 27.

In the event that only one of the relays 23 or 24 operates but not the other, for any reason, Wire 29 is con- .nected to ground through the `make contacts b of the Ioperatedrelay and the break contacts b of the released relay to register an alarm condition in equipment 27. At `the same time wire 28 is connected to ground at .make contacts a of the operated relay to register a track occupied condition. This feature is made possible by the Vtwo-frequency system, using separate energy sources `and detectors.

AIt will be obvious to those skilled in the art, that a single energysource such as generator 8 may be coupled .to..only one of the rails such as 2, with a detector such as -12 connected to the other rail 3, to register the presence or absence of a train. It is also obvious that such Asingle source, or one of the sources when two are used,

may be directzcurrent. However, alternating-current energy sources at Yfrequencies in the audio rangeare preferred to .obtain maximum coupling between the rails While a train is present. .In .both the specification and claims, a train may be a single car orlocornotive or the usual combination of them.

`While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that .this .description is made .onlyby way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A track circuit forfdetecting the presence of a train on a section of thetrack, wherein the two rails of one section are insulated'from adjoining sections at each end thereof, comprising -a .unidirectional .transmitter lincludying a source 'of `alternatingcurrent of a tirst frequency for registering an occupied'condition for said -track section.

2. The track circuit lof claim 1 wherein each detector -includes apair .of single frequency lters connected `in parallel, each detector being responsive to both the first and second frequency'respectively.

3. The .track circuit of claim 2 and a relay connected .to 4each filter, two of said relays .being vresponsive to a Ydifferent one of the tilter'frequencies respectively and having a threshold response.

4. The track circuit of claim 3 wherein the alternating current cross-coupling between the rails is altered by the `presence of a trainin a .track ksection .and .a relay ,in each detectoris activated thereby to indicate 'atrack occupied condition.

5. The track circuit of claim V3 wherein the other two relays in said detector are adapted to provide an alarm indication.

References Cited in the lle of this patent 'UNITED STATES PATENTS 1,683,709 Wenzel Sept. l1, vl1928 2,210,242 Hoppe Aug. 6, 1940 FOREIGN PATENTS 539,810 Germany Dec. 5, 1931 597,110 Germany May 17, 1934 533,423 Germany v.Tuly 27, 1936 

